The answer is the HealthyHostCount metric. This CloudWatch metric directly reveals the number of healthy targets registered with your Application Load Balancer per Availability Zone; when this count drops toward zero, the ALB has no available backend to serve traffic, forcing it to return HTTP 5xx errors even if the remaining instances show low CPU utilization. On the AWS Certified DevOps Engineer Professional DOP-C02 exam, this question tests your ability to distinguish between symptom metrics (like error rate) and root-cause metrics—a common trap is reaching for UnHealthyHostCount, which only shows the unhealthy count without indicating whether that count is causing errors, whereas a declining HealthyHostCount is the direct trigger. For a memory tip, think “Healthy Count = Can Serve; if it’s low, errors will grow.”
DOP-C02 Monitoring and Logging Practice Question
This DOP-C02 practice question tests your understanding of monitoring and logging. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A company is using an Application Load Balancer (ALB) in front of an Auto Scaling group of EC2 instances. The operations team notices that the error rate on the ALB is increasing, but the CPU utilization on the EC2 instances remains low. Which CloudWatch metric should be examined to determine if the errors are due to a lack of healthy targets?
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
HealthyHostCount
Option A is correct because HealthyHostCount indicates the number of healthy targets per Availability Zone. If it drops, the ALB may return errors. Option B (UnHealthyHostCount) shows unhealthy hosts but not the direct cause of errors. Option C (RequestCount) measures total requests. Option D (TargetResponseTime) measures latency.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
UnHealthyHostCount
Why it's wrong here
Incorrect. UnHealthyHostCount shows unhealthy hosts but does not directly explain error rate changes.
✗
RequestCount
Why it's wrong here
Incorrect. RequestCount measures total requests, not errors.
✓
HealthyHostCount
Why this is correct
Correct. HealthyHostCount shows the number of healthy targets. A decrease indicates fewer available targets, which can cause errors.
Related concept
Read the scenario before looking for a memorised answer.
✗
TargetResponseTime
Why it's wrong here
Incorrect. TargetResponseTime measures latency, not error rate.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Trap categories for this question
Command / output trap
Incorrect. UnHealthyHostCount shows unhealthy hosts but does not directly explain error rate changes.
Detailed technical explanation
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
KKey Concepts to Remember
Read the scenario before looking for a memorised answer.
Find the constraint that changes the correct option.
Eliminate answers that are true in general but not in this case.
Use explanations to understand the rule behind the answer.
TExam Day Tips
→Underline the problem statement mentally.
→Watch for words such as best, first, most likely and least administrative effort.
→Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
Monitoring and Logging — This question tests Monitoring and Logging — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: HealthyHostCount — Option A is correct because HealthyHostCount indicates the number of healthy targets per Availability Zone. If it drops, the ALB may return errors. Option B (UnHealthyHostCount) shows unhealthy hosts but not the direct cause of errors. Option C (RequestCount) measures total requests. Option D (TargetResponseTime) measures latency.
What should I do if I get this DOP-C02 question wrong?
Identify which DOP-C02 exam domain this question belongs to, then review the specific concept being tested. Practise related questions in that domain and focus on understanding why each wrong answer is tempting — not just why the correct answer is right.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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This DOP-C02 practice question is part of Courseiva's free Amazon Web Services certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the DOP-C02 exam.
Question Discussion
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